For the purposes of improving the stability thereof when anchoring bone screws, in the case of bone screws in the form of pedicle screws for example, they can be additionally fixed in the bone with the aid of bone cement. In principle thereby, bone cement can be injected into a pre-prepared hole in the bone. Thereafter, the screw is then screwed into the cement filling forming in the hole.
It is advantageous however to use a hollow screw which has a longitudinal channel extending from its proximal end to its distal end. After the screw has been implanted in the bone, the cement is injected through the longitudinal channel in the screw only after the implantation process. Screws are known which have lateral cement outlet openings that are connected to the longitudinal channel in fluid-conveying manner. As an option, the distal end of the screw could also be closed. The employment of screws of this type has the particular advantage that the cement can be injected in a controlled manner, and a uniform coating of cement can be formed around the screw commencing from the cement outlet openings.
From experience, cement does not normally emerge from the tip even in the case where the bone screw is open at the distal end if suitable lateral cement outlet openings have been provided. The reason for this is that the flow resistance for the bone cement is higher at the tip in dependence on the configuration of the lateral cement outlet openings. Nevertheless, there is a danger that the lateral cement outlet openings may become clogged by bone material when driving the screw into the bone. In practice, this cannot really be avoided so that one cannot completely eliminate a certain danger of cement emerging from the distal end. It can be particularly critical for example, if an osteoporosis screw being inserted into a vertebral body breaks through the contralateral bone of the vertebral body and the injected cement then, in the most unfavourable case, emerges ventrally of the vertebral body. In the course of biomechanical investigations, it could be established that hollow screws not using a K-wire become partially clogged and as a result the process of injecting cement is very difficult in certain circumstances.
Consequently, it would be desirable to provide a surgical K-wire and also a surgical screw system for minimizing emergence of bone cement at the distal end in the case of a completely channeled-out bone screw being guided by the K-wire.